1. Field of the Invention
The present invention relates to an SOA-PLC hybrid integrated polarization diversity circuit and a method for manufacturing the same, the circuit including a semiconductor optical amplifier (SOA) and a polarization beam splitter (PBS) which is a planar lightwave circuit (PLC).
2. Description of the Related Art
In recent years, with the increase of data volume in optical communication networks, compact and low-cost optical devices have been demanded. A trend is currently changing such that an optical waveguide device technique based on a photonic integrated circuit (PIC) technology is dominating a conventional technique of combining individual optical components.
In an optical communication network, it is preferable from a practical viewpoint that an optical waveguide device should have a polarization dependence of 0.1 dB or lower. In order to solve a problem with the polarization dependence in an optical device, a polarization diversity circuit is used.
A polarization independent SOA module for solving the problem with polarization dependent gain (PDG) of an SOA by use of a polarization diversity circuit is disclosed in K. Morito and S. Tanaka, “Record High Saturation Power (+22 dBm) and Low Noise FIG. (5.7 dB) Polarization-Insensitive SOA Module,” IEEE PHOTONICS TECHNOLOGY LETTERS, 17, 6, 1298-1300, (2005) (hereinafter Non-patent Literature 1). As shown in FIG. 14, the polarization independent SOA module uses a circulator 1409 having three ports 1401 to 1403, lenses 1404, a semitransparent mirror 1405 serving as a PBS, a half-wave plate 1406, mirrors 1407, and an SOA 1408, which are spatially-separated individual optical components.
However, the polarization independent SOA module disclosed in Non-patent Literature 1 uses the spatially-separated individual optical components, and thus has a large module size as a whole. In addition, since the module disclosed in Non-patent Literature 1 uses the optical components such as the semitransparent mirror 1405 and the mirrors 1407, formation of the module shown in FIG. 14 requires user's optical axis adjustment among the optical components, which is very troublesome. Hence, application such as incorporation of the module into another device is difficult. For this reason, it is believed that commercial use of the module disclosed in Non-patent Literature 1 is difficult.